The long term goal is to understand why a diversity of well regulated membrane lipids are needed for cellular functions; some of these lipids are apparently selected for their physical rather than their chemical properties. Phospholipids of active membranes are often maintained at a state which is marginally stable in the bilayer form. These lipids prefer to form high curvature structures if not constrained to the bilayer form at the cost of bending energy. Certain membrane functions are known to be regulated by the bending energy of the lipid bilayers, but the quantitative relationship is not clear. The specific aims are: (1) to measure the bending stress in several phospholipid bilayers by the geometry of their self-assembly forms; (2) to determine the relationship between macroscopic bending stress and microscopic molecular packing measurements by several spectroscopic methods; (3) to investigate the stability of, and the nature of defects in supported and unsupported monolayers of lipids with high bending stress; and (4) to study the functions of protein kinase C and a synthetic ion channel peptide in a lipid environment as functions of bending stress of the bilayers. The techniques used include X-ray diffraction; quasi-elastic light scattering; electron, fluorescence and atomic force microscopy; fluorescence and NMR spectroscopy, monolayer and planar bilayer techniques; as well as peptide synthesis and functional assays. Understanding this general but often overlooked mechanism of functional regulation will not only enrich our basic knowledge in cellular functions and dysfunctions, but also help the designing and fabrication of biosensors and other biomedical devices utilizing stable lipid monolayers.